1. Field of the Invention
This invention relates to clutches with a divided flywheel apparatus having a first centrifugal mass connected to a driving mechanism and a second centrifugal mass engaged with the first centrifugal mass by means of a torsional vibration damper. The second centrifugal mass is capable of a limited relative rotation with respect to the first centrifugal mass, and the apparatus further includes a damping device which contains at least one vibration damper, by means of which, under specified operating conditions, a frictional connection can be established between the two centrifugal masses.
2. Background Information
Such a flywheel apparatus for a clutch mechanism is, for example, known through German Patent No. 39 41 251 A1. Between a first centrifugal mass and a second centrifugal mass which can rotate in relation to the first centrifugal mass, there is a torsional vibration damper which consists of a torsion spring system and a friction device. Axially between the two centrifugal masses there is also a vibration damper of a damping device which, at a pre-determined rotational speed, preferably at the speed of rotation corresponding to the resonance speed through which the system passes during startup and shutdown of the internal combustion engine, is actuated so that a predetermined moment can be transmitted from the first centrifugal mass to the second centrifugal mass. It thereby becomes possible, when the system passes through the resonance speed, to suppress extreme relative rotations of the two centrifugal masses relative to one another by means of the friction action of the vibration damper, and thereby to prevent springs of the torsion spring system interposed between the two centrifugal masses from being compressed all the way, which can result in damage to the system.
According to the above-referenced unexamined patent application, the friction moment between the centrifugal masses exerted by the vibration damper can be set at an arbitrarily high value, whereby the setting can be achieved on one hand by selecting an axial spring which applies a pressure to the vibration damper, and on the other hand by means of the disengagement force exerted on the clutch housing of the friction clutch. As soon as the axial spring for the vibration damper is installed in the friction clutch, there are essentially no further possibilities for adjusting the vibration damper, since the release force which is applied to an application means, such as by a membrane spring for release of the clutch, is defined as a function of this membrane spring, and consequently essentially always acts with a constant strength on the clutch housing of the friction clutch for the axial displacement of the friction clutch toward the axial spring.
The flywheel apparatus disclosed in the above-referenced unexamined patent application is a so-called "dry" model, requiring no lubricant, such as grease, etc. In contrast, German Patent No. 41 28 868 A1, which corresponds to U.S. Pat. No. 5,307,710, discloses a divided flywheel apparatus in which a torsional vibration damper between the two circumferential masses, which vibration damper acts in the circumferential direction, is located inside a sealed chamber which is filled with viscous medium. The viscous medium can be used to achieve a damping of a relative rotation of the two centrifugal masses with respect to one another, wherein the damping is proportional to velocity. As a result of this arrangement, a torsion spring system can be installed in the circumferential area with extremely long-stroke springs. With such a torsion spring system, the resonance frequency of the flywheel apparatus can be set close to the starting speed of a driving mechanism, such as that of an internal combustion engine, so that when the system passes through the resonance frequency, e.g. during the starting procedure, the energy supplied by the driving mechanism is too low to cause any damage to the flywheel apparatus. As soon as this very low resonance frequency has been passed through during the starting procedure, the frequency does not recur during further operation of the driving system, since the frequency is significantly below the idle speed. A flywheel apparatus with a chamber for viscous medium therefore does not necessarily require an additionally active vibration damper between the two centrifugal masses. However, on account of the presence of the chamber, the flywheel apparatus is significantly larger than the above-mentioned "dry" model, and since means are necessary to seal the chamber, it is also significantly more expensive to provide such an arrangement in which a viscous medium needs to be sealed.
To damp torsional vibrations, one design solution is known in which a friction clutch is combined with a device which positions a clutch engagement or release mechanism by means of the actuating drive of an automatic clutch. Such a device is illustrated and described, for example, in German Patent No. 36 24 755 A1. The actuating drive is regulated so that torsional vibrations, which can cause noises for example, are damped by a predetermined slip between the friction linings of the clutch plate and the corresponding clutch elements.
One disadvantage of such a mode of operation of the friction clutch is that the operating ranges in which slip is used to damp vibrations are relatively large. Since these ranges also include operating ranges where high torque loads are experienced, the result is a high degree of wear on the linings and the generation of a large amount of heat from this mode of operation.